Oil supply structure for reducing friction of cam shaft

ABSTRACT

An oil supply structure for reducing friction of a cam shaft attached to a valve train of an automotive engine is disclosed. An oil supply hole formed in a cam shaft is, repeatedly connected and disconnected to a cylinder head oil supply hole during the rotation of the cam shaft. An oil pocket is established in the form of a concave groove in a section in the circumferential direction on an inner circumferential surface of a cam cap assembled on the top of the cam shaft so as to supply oil to the oil pocket only when the cylinder head oil supply hole is connected to the cam shaft oil supply hole. It is thus possible to supply oil to the oil pocket through the cam shaft oil supply hole at specific points of time and, simultaneously, to sufficiently ensure the sealing width in other regions than the oil pocket, thus reducing oil loss and obtaining a more efficient friction reduction.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2006-0112093, filed on Nov. 14, 2006, the entire disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oil supply structure for reducing friction of a cam shaft and, more particularly, to such an oil supply structure attached to a valve train of an internal combustion engine.

2. Description of Related Art

In general, the respective cylinders of an automotive engine comprise at least two valves divided into an intake valve and an exhaust valve. The intake valve is opened just before an intake stroke starts to intake a mixture of air and fuel into the cylinder and the exhaust valve is opened just before an exhaust stroke starts to exhaust combustion gas out of the cylinder.

The valves are operated by a valve train configured to make the intake valve and the exhaust valve open and close at accurate points of time by a crank shaft rotated by piston movement.

The valve train may comprise a cam shaft, on which a plurality of cams are established along with an axis, a push rod, a rocker arm transmitting the movement of the cams or of a push rod, a tappet (or a roller) forwarding the movement of cam lobes to the push rod, etc., and means that control intake and exhaust air amounts and intake and exhaust times in accordance with the region of the engine rotational speed.

Meanwhile, in sliding portions, such as the piston sliding up and down in the cylinder, or in rotational portions, such as the crank shaft and the cam shaft, frictional heat is generated by direct friction with metals and thereby the friction surface is worn away or melted down, thus causing an engine trouble.

To prevent such engine troubles, oil is supplied to the friction surface of metals so that solid friction generated on the friction surface of metals is converted into a liquid friction by an oil film, thus providing a smooth operation. Because of the importance of lubrication in an internal combustion engine, a variety of oil supply structures have been developed. However, conventional oil supply structures can have some drawbacks.

First, since oil is typically introduced through a hollow flow path in the cam shaft, the peripheral structure for supplying oil to the hollow flow path of the cam shaft is complicated and has limitations in terms of design due to the complicated peripheral structure for supplying oil to the hollow flow path of the cam shaft.

Moreover, when typical conventional structures are applied to a small sized engine, an oil pressure reduction may occur that deteriorates the friction reduction performance, and a hollow cam shaft applied thereto would be a factor that increases the manufacturing cost.

Furthermore, since the amount of oil supplied to the oil groove in conventional structures is large and the amount of oil exhausted to the outside through the oil groove is also large, a large quantity of oil is consumed unnecessarily.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide an oil supply path with a solid cam shaft, an oil supply hole to be connected to an oil supply hole of the cylinder head is established on the solid cam shaft, an oil pocket formed in a predetermined section of the inner circumferential surface of a cam cap assembled on the top of the cam shaft so as to supply oil to the oil pocket at specific points of time when the oil supply holes of the cam shaft and the cylinder head are connected to each other during the rotation of the cam shaft and, at the same time, to sufficiently ensure the sealing width in other regions than the oil pocket, thus preventing the oil loss over a necessary amount and obtaining a more efficient effect of friction reduction.

In an exemplary embodiment of the present invention, there is provided an oil supply path for reducing friction of a cam shaft comprising: a cylinder head oil supply hole, established inside a cylinder head, of which an outlet is positioned on an inner circumferential surface of a journal part bearing-supporting the cam shaft and an inlet is connected to an oil gallery in the cylinder head; a cam shaft oil supply hole, formed on the cam shaft supported by the journal part of the cylinder head, penetrated at a position to be connected to the outlet of the cylinder head oil supply hole; and an oil pocket, established only in a specific section of a predetermined length in the circumferential direction on an inner circumferential surface, which is a friction surface with the cam shaft, of a semicircular cam cap assembled on the cylinder head over the cam shaft, so as to connect opening portions on one end and on the other end of the cam shaft oil supply hole with each other, thus supplying oil to the oil pocket from the cam shaft oil supply hole.

The oil pocket may be arranged to connect the opening portion on one end of the cam shaft oil supply hole to the opening portion on the other end of the cam shaft oil supply hole when the opening portion on one end of the cam shaft oil supply hole is coupled to the outlet of the cylinder head oil supply hole.

Moreover, the oil pocket can be established in the inner circumferential surface of the semicircular cam cap from a position, which meets a hole central extension line of the opening portion on one end of the cam shaft oil supply hole at the point of time when the opening portion on the other end of the cam shaft oil supply hole meets the outlet of the cylinder head oil supply hole, to a position, which meets the hole central extension line of the opening portion on one end of the cam shaft oil supply hole at the point of time when the opening portion on the other end of the cam shaft oil supply hole is completely out of the outlet of the cylinder head oil supply hole.

The oil pocket also may be arranged in a specific section between a position corresponding to an angle of about 55° and a position corresponding to angle of about 85° from an end point in the inner circumferential surface of the semicircular cam cap.

In a further alternative embodiment of the present invention, an oil supply structure for an engine having a cam shaft carried in a journal between a cam cap and cylinder head includes first and second oil supply holes and an oil pocket. The first oil supply hole is defined in the cylinder head and communicates between the journal and an oil gallery. The second oil supply hole is defined through the cam shaft and positioned to periodically align with the first oil supply hole upon rotation of the cam shaft. The oil pocket is formed in the cam cap and positioned to periodically receive oil from the oil gallery through the first and second oil supply holes upon rotation of the cam shaft. The cam shaft, cylinder head and cam cap may include plural aligned oil supply holes and oil pockets.

The oil pocket may have a width that is substantially the same as the diameter of the second oil supply hole, and the oil pocket may have a length that extends around a part of an inner circumference of the journal in the cam cap. The length of the oil pocket may be greater than the diameter of the oil pocket. In one such embodiment, the oil pocket extends for a length of about 30° around an inner circumference of the cam cap. In a further embodiment, the length of the oil pocket extends from a position about 55° from an end point of the cam cap to a position about 85° from the same end point.

In yet another alternative embodiment, a cylinder head defines a first oil supply hole therein communicating with an oil gallery, a cam shaft journal is formed in the cylinder head with the first oil supply hole communicating with the journal, a cam shaft is disposed in the journal and defines a second oil supply hole extending therethrough in a position disposed to periodically align with the first oil supply hole upon rotation of the cam shaft, and a cam cap covers the cam shaft and forms an upper journal portion around the cam shaft with the cam cap defining an oil pocket therein disposed to periodically communicate with the oil gallery through the first and second oil supply holes upon rotation of the cam shaft and second oil supply hole therein. The cam shaft, cylinder head and cam cap may define plural sets of aligned first and second oil supply holes and oil pockets, each set spaced longitudinally along the cam shaft, cylinder head and cam cap.

In this embodiment, the oil pocket may also have a width substantially the same as the diameter of the second oil supply hole, and the oil pocket may also have a length that extends around a part of an inner circumference of the journal in the cam cap. The oil pocket may extend for a length of about 30° around an inner circumference of the cam cap, wherein the length of the oil pocket extends from a position about 55° around an inner circumference of the cam cap from point were the cam cap meets the cylinder head to a position about 85° from that point. The cam cap may meet cylinder head along a substantially horizontal plan that substantially bisects the cam shaft or along a plane at another orientation.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will be described with reference to certain exemplary embodiments thereof illustrated the attached drawings in which:

FIG. 1 is a cross-sectional view depicting an oil supply path of a cam shaft in accordance with an embodiment of the present invention;

FIG. 2 is a perspective view depicting an oil supply hole penetrating through a cam shaft in an oil supply path in accordance with an embodiment of the present invention;

FIG. 3 is a plan view depicting a cam shaft in which a plurality of oil supply holes of FIG. 8 are established penetrated at predetermined positions of the cam shaft;

FIG. 4 is a plan view depicting an oil pocket of a cam cap in an oil supply path in accordance with an embodiment of the present invention;

FIG. 5 is a cross-sectional view taken along with line ‘A-A’ of FIG. 4;

FIGS. 6 and 7 are diagrams depicting states where an oil pocket is opened and closed by an oil supply hole of a cam shaft in an oil supply structure in accordance with embodiments of the present invention, in which FIG. 6 depicts a state where the oil pocket starts to be opened and FIG. 7 depicts a state where the oil pocket starts to be closed; and

FIG. 8 is a graph illustrating measurement results of crank torques required in driving intake and exhaust cams in an example in accordance with an embodiment of the present invention and a conventional structure.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, exemplary embodiments of the present invention will now be described in detail with reference to the attached drawings.

As depicted in FIG. 1, an oil supply path in the embodiment of the present invention can be applied to a solid cam shaft 120 inserted into the inner circumferential surface of a journal part 111 of a cylinder head 110 and supported therein. A cam cap 114 is assembled on the cylinder head 110 by bolts, not depicted, over the cam shaft 120.

As an oil supply path in the cylinder head 110, through which oil is supplied to reduce friction of the cam shaft 120, an oil supply hole 113 is formed in the cylinder head 110. An outlet of hole 113 is positioned on the inner circumferential surface of the journal part 111 supporting the cam shaft 120 and an oil gallery 112 formed in the cylinder head 110 is connected to the opposite inlet of the oil supply hole 113 and thereby the oil supply hole 113 has a structure in which it is connected to the oil gallery 112 in the cylinder head 110. Moreover, an oil supply hole 121 is established penetrating through the respective portions supported by the journal part 111 of the cylinder head 110 in the cam shaft 120, as depicted in FIGS. 2 and 3.

Referring to FIG. 3, it can be seen that the oil supply holes 121 are formed penetrating through four supported portions established on the cylinder head 110. The oil supply hole 121 is disposed to communicate with the oil supply hole 1113 of the cylinder head 110. That is, when an opening portion on one end of the oil supply hole 121 of the cam shaft 120 meets the outlet of the cylinder head oil supply hole 1113 while the cam shaft 120 rotates, two oil supply holes 113 and 121 on both sides communicate with each other, thus opening the oil supply path between the cylinder head 110 and the cam shaft 120.

An oil pocket 115 of a predetermined length is established in the form of a concave groove in a section in the circumferential direction on a friction surface between the outer circumferential surface of the cam shaft 120. The cam cap 114 assembled on the cylinder head 110 by bolts, i.e., on the inner circumferential surface of the cam cap 114, as depicted in FIGS. 4 and 5. The oil pocket 115 is formed at a position communicating with the oil supply hole 121 of the cam shaft 120 and its width corresponds to the diameter of the oil supply hole 121 of the cam shaft 120.

For example, an oil supply hole 121 of 3 mm in diameter is established on the cam shaft 120 and an oil pocket 115 of 3 mm in width is arranged on the inner circumferential surface of the cam cap 114. Here, the width direction position of the oil pocket 115 is set to meet the opening portion on one end of the cam shaft oil supply hole 121 completely in the inner circumferential surface of the cam cap 114 so that the whole opening portion on the end of the cam shaft oil supply hole 121 is completely opened by the oil pocket 115 at a specific point of time when the whole opening portion on the end of the cam shaft oil supply hole 121 meets the oil pocket 115 of the cam cap 114 completely to open a side of the oil pocket 115 while the cam shaft 120 rotates.

Referring to FIG. 4, it can be seen that the oil pocket 115 is established in the middle of the inner circumferential surface of the cam cap 114 in the width direction. Moreover, an oil pocket 115 in accordance with the present invention is established in a section of a predetermined length on the inner circumferential surface of the cam cap 114 in the circumferential direction.

The attached FIGS. 6 and 7 are diagrams depicting states where an oil pocket 115 is opened and closed by an oil supply hole 121 of a cam shaft 120 in an oil supply structure in accordance with the present invention, in which FIG. 6 depicts a state where the oil pocket 115 starts to be opened and FIG. 7 depicts a state where the oil pocket 115 starts to be closed. The oil pocket 115 starts to be opened when it meets the opening portion on the end of the cam shaft oil supply hole 121 while the cam shaft 120 rotates, whereas, the oil pocket 115 starts to be closed when the opening portion on the end of the cam shaft oil supply hole 121 is out of the oil pocket 115.

In a state where the oil pocket 115 is opened by the opening portion on one end of the cam shaft oil supply hole 121, the opening portion on the other end of the cam shaft oil supply hole 121 is connected to the outlet of the cylinder head oil supply hole 113. Accordingly, an oil supply path is formed from the oil gallery 112 of the cylinder head 110, the oil supply hole 113 of the cylinder head 110, the oil supply hole 121 of the cam shaft 120 and the oil pocket 115 of the cam cap 114 in turn.

While the cam shaft 120 rotates, the respective portions of the oil supply path from the oil gallery 112 of the cylinder head 110 to the oil pocket 115 of the cam cap 114 are connected to one another so that the oil supplied from the oil gallery 112 to the oil pocket 115 lubricates the cam shaft 120 to reduce friction.

The number of times that the respective portions of the oil supply path are connected to one another to supply oil, i.e., the number of times that the oil supply path from the oil supply hole 113 of the cylinder head 110 to the oil pocket 115 of the cam cap 114, is two times during one rotation of the cam shaft 120. Here, the opening portion on one end of the cam shaft oil supply hole 121 and the opening portion on the other end of the cam shaft oil supply hole 121 are to open the outlet of the oil supply hoe 113 and the oil pocket 115 of the cam cap 114 in turn.

The oil supply path is thus repeatedly opened and closed during the rotation of the cam shaft 120 and oil is supplied at the very point of time when the oil supply path is opened. Moreover, since oil is not supplied to the cam shaft 120 at all times, but two times when the oil supply path is opened for one rotation of the cam shaft 120, it is possible to reduce unnecessary oil consumption.

In establishing the oil pocket 115 on the inner surface of the cam cap 114, the oil pocket 115 is arranged on the inner circumferential surface of the semicircular cam cap 114 long in the circumferential direction as depicted in FIG. 5. However, it is positioned only in a specific section between a position corresponding to an angle of about 55° and a position corresponding to angle of about 85° from an end point of the cam cap 114.

Here, the position corresponding to an angle of about 55° is directed to a position that meets a hole central extension line L of the opening portion on one end of the cam shaft oil supply hole 121 at the point of time when the opening portion on the other end of the cam shaft oil supply hole 121 meets the outlet of the cylinder head oil supply hole 113. The position corresponding to an angle of about 85° is directed to a position that meets the hole central extension line L of the opening portion on one end of the cam shaft oil supply hole 121 at the point of time when the opening portion on the other end of the cam shaft oil supply hole 121 is completely out of the outlet of the cylinder head oil supply hole 113.

During the rotation of the cam shaft 120, oil is supplied from the cylinder head 110 to the oil pocket 115 of the cam cap 114 only for a short time from the point of time when the opening portion on one end of the cam shaft oil supply hole 121 starts to meet the outlet of the cylinder head oil supply hole 113, that is, from the point of time when the outlet of the cylinder head oil supply hole 113 is opened by the opening portion on one end of the oil supply hole 121, to the point of time when the opening portion on one end of the cam shaft oil supply hole 121 is completely out of the outlet of the cylinder head oil supply hole 113, that is, to the point of time when the outlet of the cylinder head oil supply hole 113 is completely closed.

According to embodiments of the present invention configured as described above, the oil pocket 115 is established only in a predetermined section of the cam cap 114 to supply oil only at specific points of time (two times for one rotation of the cam shaft) through the oil supply holes 121 penetrating through the cam shaft 120 and, at the same time, to ensure the sealing width sufficiently in other regions than the oil pocket 115, thus preventing the oil loss over a necessary amount.

That is, it is possible to established an oil supply path, in which a groove corresponding to the oil pocket 115 is formed over the whole section of 360° along with the circumferential direction on the inner surface of the cam cap surrounding the cam shaft and the inner surface of the cylinder head journal part and the oil supply hole of the cylinder head is connected to one side of the groove; however, in this case, a large quantity of oil is supplied to the whole groove of 360° through the oil supply hole at all times, thus consuming a large quantity of oil.

Accordingly, the oil pocket 115 of the present invention is established only in a specific section so that oil is supplied only at the very point of time when the oil supply hole 121 of the cam shaft 120 and the oil supply hole 113 of the cylinder head 110 are connected (opened) to each other. Accordingly, it is possible to obtain effects of reducing friction and, at the same time, decreasing the oil consumption remarkably, and ensure an efficient friction reduction.

Especially, accordingly to the structure in which the groove is formed in the whole section, the sealing width between the friction surfaces (the width of other areas than the groove area) is reduced and thereby the oil loss becomes larger.

Accordingly, in the structure where the width of the cylinder head journal part 111 and that of the cam cap 114 are small (for example, in an engine of a width of 12 mm or less), a groove can not be applied thereto to ensure a sufficient sealing width. However, according to the oil pocket 115 established in a specific section of the present invention, it is possible to ensure the sealing width sufficiently in the areas other than the oil pocket 115, thus achieving the reduction of oil loss and the efficient friction reduction.

The following table 1 depicts results of a friction torque test, in which a comparative example corresponds to the structure in which oil is supplied between the outer circumferential surface of the cam shaft and the inner circumferential surface of the cam cap and the cylinder head journal part according to a conventional design and an example is directed to an embodiment of the present invention. It can be understood from the table 1 that the friction torque reduction more than 30% is ensured in the whole area of the engine to which an embodiment of the present invention is applied.

TABLE 1 Test Results 1000 rpm Friction 2000 rpm Torque Reduction Rate Friction Torque Reduction Rate Examples (Nm) (%) (Nm) (%) Conventional 1.48 0.77 Invention 1.01 32↓ 0.48 38↓

Moreover, the attached FIG. 8 is a graph illustrating measurement results of crank torques required in driving intake and exhaust cams in the invention and conventional structure, through which it can be found that the crank torques in the example of the present invention are considerably reduced compared with the conventional structure.

As described above, according to the oil supply path for reducing friction of the cam shaft in accordance with the present invention, the oil pocket is established only in a predetermined section of the cam cap to supply oil only at specific points of time (two times for one rotation of the cam shaft) through the oil supply holes penetrating through the cam shaft and, at the same time, to ensure the sealing width sufficiently in other regions than the oil pocket, thus preventing the oil loss over a necessary amount and obtaining a more efficient effect of friction reduction.

Moreover, since the solid cam shaft is applied to the present invention, it is possible to solve various problems caused when applying the hollow cam shaft, such as the complication of the structure, limitations in design, increase in manufacturing cost, etc.

As above, exemplary embodiments of the present invention have been described and illustrated, however, the present invention is not limited thereto, rather, it should be understood that various modifications and variations of the present invention can be made thereto by those skilled in the art without departing from the spirit and the technical scope of the present invention as defined by the appended claims. 

1. An oil supply path for reducing friction of a cam shaft, comprising: a cylinder head oil supply hole, defined inside a cylinder head having an outlet positioned on an inner circumferential surface of a journal part bearing-supporting the cam shaft and an inlet is connected to an oil gallery in the cylinder head; a cam shaft oil supply hole formed on the cam shaft supported by the journal part of the cylinder head and penetrating at a position to communicate with the outlet of the cylinder head oil supply hole; and an oil pocket formed with a predetermined length in the circumferential direction on an inner circumferential surface, which is a friction surface with the cam shaft, of a semicircular cam cap assembled on the cylinder head over the cam shaft, so as to connect opening portions on one end and on the other end of the cam shaft oil supply hole with each other, thus supplying oil to the oil pocket from the cam shaft oil supply hole.
 2. The oil supply path for reducing friction of a cam shaft as recited in claim 1, wherein the oil pocket is arranged to connect the opening portion on one end of the cam shaft oil supply hole to the opening portion on the other end of the cam shaft oil supply hole when the opening portion on one end of the cam shaft oil supply hole is coupled to the outlet of the cylinder head oil supply hole.
 3. The oil supply path for reducing friction of a cam shaft as recited in claim 1 or claim 2, wherein the oil pocket is established in the inner circumferential surface of the semicircular cam cap from a position, which meets a hole central extension line of the opening portion on one end of the cam shaft oil supply hole at the point of time when the opening portion on the other end of the cam shaft oil supply hole meets the outlet of the cylinder head oil supply hole, to a position, which meets the hole central extension line of the opening portion on one end of the cam shaft oil supply hole at the point of time when the opening portion on the other end of the cam shaft oil supply hole is completely out of the outlet of the cylinder head oil supply hole.
 4. The oil supply path for reducing friction of a cam shaft as recited in claim 3, wherein the oil pocket is arranged in a specific section between a position corresponding to an angle of about 55° and a position corresponding to angle of about 85° from an end point in the inner circumferential surface of the semicircular cam cap.
 5. An oil supply structure for an engine having a cam shaft carried in a journal between a cam cap and cylinder head, the oil supply structure comprising: a first oil supply hole defined in the cylinder head and communicating between said journal and an oil gallery; a second oil supply hole defined through said cam shaft and positioned to periodically align with the first oil supply hole upon rotation of the cam shaft, and an oil pocket formed in said cam cap and positioned to periodically receive oil from said oil gallery through the first and second oil supply holes upon rotation of the cam shaft.
 6. The oil supply structure of claim 5, wherein: the second oil supply hole has a diameter and the oil pocket has a width substantially the same as the diameter of the second oil supply hole; and the oil pocket has a length that extends around a part of an inner circumference of the journal in the cam cap.
 7. The oil supply structure of claim 6, wherein said length of the oil pocket is greater than said diameter of the oil pocket.
 8. The oil supply structure of claim 7, wherein the oil pocket extends for a length of about 30° around an inner circumference of the cam cap.
 9. The oil supply structure of claim 8, wherein the length of the oil pocket extends from a position about 55° from an end point of the cam cap to a position about 85° from said end point.
 10. The oil supply structure of claim 6, wherein said cam shaft, cylinder head and cam cap include plural aligned oil supply holes and oil pockets.
 11. An oil supply structure for an engine, comprising: a cylinder head defining a first oil supply hole therein communicating with an oil gallery; a cam shaft journal formed in the cylinder head, said first oil supply hole communicating with said journal; a cam shaft disposed in said journal and defining a second oil supply hole extending therethrough in apposition disposed to periodically align with the first oil supply hole upon rotation of the cam shaft; and a cam cap covering the cam shaft and forming an upper journal portion around said cam shaft, said cam cap defining an oil pocket therein disposed to periodically communicate with the oil gallery through said first and second oil supply holes upon rotation of the cam shaft and second oil supply hole therein.
 12. The oil supply structure of claim 11, wherein: the second oil supply hole has a diameter and the oil pocket has a width substantially the same as the diameter of the second oil supply hole; and the oil pocket has a length that extends around a part of an inner circumference of the journal in the cam cap.
 13. The oil supply structure of claim 12, wherein the oil pocket extends for a length of about 30° around an inner circumference of the cam cap.
 14. The oil supply structure of claim 13, wherein the length of the oil pocket extends from a position about 55° around an inner circumference of the cam cap from point were the cam cap meets the cylinder head to a a position about 85° from said point.
 15. The oil supply structure of claim 14, wherein said cam cap meets said cylinder head along a substantially horizontal plan that substantially bisects the cam shaft.
 16. The oil supply structure of claim 11, wherein said cam shaft, cylinder head and cam cap define plural sets of aligned first and second oil supply holes and oil pockets, each said set spaced longitudinally along the cam shaft, cylinder head and cam cap. 